This invention pertains to an in situ oil recovery method, and more specifically to a method for recovering bitumen from a subterranean formation of heavy oil sands.
Heavy oil sand, such as tar sand, deposits are located in the western portion of the United States; northern Alberta, Canada; Venezuela and in locations in Europe and Asia. For example, the Athabasca tar sand deposits in Alberta, Canada contain over 700 billion barrels of petroleum of a highly bituminous character.
The extremely high viscosity of the heavy oil from these sands, i.e. about 100,000 centipoises to over 1,000,000 centipoises at formation temperatures in the range of about 40.degree.-125.degree. F. makes impossible the recovery of bitumen by ordinary methods. However, the viscosity of the oil may be reduced to 10 centipoises or less by raising the temperature by several hundred degrees. The sand is generally a fine or medium grain predominantly quartz material. The individual grains are coated with a water, and enveloped with a bitumen film. Bituminous petroleum fills at least a portion of the void space between touching grains of sand. The sand grains are packed to a void volume of about 35%. This corresponds to a bitumen-sand mixture of roughly 83 wt. % sand.
Recovery of oil by a combination of low temperature oxidation and hot water or steam injection is disclosed in coassigned U.S. Pat. No. 3,976,137. The recovery of viscous oil using pressurization cycles is disclosed in coassigned U.S. Pat. No. 4,127,172. A thermal method for recovering oil employing steam injection and the introduction of a noncondensing gas which is substantially free of oxidizing components is disclosed in U.S. Pat. No. 3,782,470. Introducing an alkali solution into a formation of tar sand to create fractures and to leach and emulsify and the periodic reverse flush of the formation by passing a slug of alkaline solution through the production well is disclosed in U.S. Pat. No. 3,279,538. In situ recovery in which steam and a solvent are cyclically and continuously injected into tar sands is disclosed in U.S. Pat. No. 3,946,810.
While there are many proposed in situ methods for recovering heavy oil from heavy oil sands, there remains a need for an efficient and economical method such as provided herein for recovering viscous bituminous petroleum from subterranean deposts of heavy oil sands.